A comprehensive study on the dual species biofilm formation of clinical Staphylococcus aureus and Candida albicans strains from the same origins

Biofilms, complex microbial communities that enhance pathogen survival in hostile environments, are integral to chronic infections and often exhibit polymicrobial interactions that influence disease outcomes. Among these, <i>Staphylococcus aureus</i> and <i>Candida albicans</i> co-infections are of particular clinical significance due to their synergistic mechanisms, resulting in invasive and treatment-resistant infections. This study investigated the interaction dynamics of <i>S. aureus</i> and <i>C. albicans</i> in both planktonic and biofilm states, focusing on growth dominance, biofilm formation, and structural adaptations under different conditions. Results revealed that <i>C. albicans</i> dominated in planktonic co-culture, suppressing <i>S. aureus</i> growth, whereas biofilm conditions favored mutual adaptation, with hyphae-competent <i>C. albicans</i> forming dual-species biofilms with <i>S. aureus</i> that accumulated substantial biomass, thereby enhancing biofilm cohesion and resistance. Compared to yeast cells in YPD, hyphal growth induced by RPMI substrates significantly augmented biofilm formation across the early, proliferating, and mature stages. Colonization order influenced biofilm architecture and interspecies interactions, with highly mature biofilms exhibiting dense network structures and increased <i>C. albicans</i> hyphal formation. Mechanical measurements revealed an elastic modulus of up to 10 Pa, indicating enhanced biofilm rigidity and structural integrity. Notably, the hyphal contribution of <i>C. albicans</i> was stage-dependent-facilitating <i>S. aureus</i> proliferation during proliferating phase. These findings underscore the complexity of <i>S. aureus</i>-<i>C. albicans</i> interactions and highlight potential targets for disrupting biofilm-associated chronic infections.